Peter J. Gardner

Infrared spectroscopic comparison of the chemisorbed species from ethene, propene, but-1-ene and cis- and trans-but-2-ene on Pt(111) and on a platinum/silica catalyst

The chemisorption of ethene, propene, but-1-ene, cis- and trans-but-2-ene and but-2-yne has been studied on a Pt(111) surface using reflection absorption infrared spectroscopy (RAIRS). The results have been compared with transmission infrared spectra of the alkenes adsorbed on a finely divided impregnated Pt/SiO2 catalyst.On the Pt(111) surface ethene, propene and but-1-ene are adsorbed in the corresponding n-alkylidyne form CH3(CH2)nCPt3(n= 0, 1, 2) at room temperature. The cis- and trans-but-2-enes are adsorbed in the form of but-2-yne bonded to the surface in a di-σ/π fashion, as was confirmed by adsorption of but-2-yne itself.The room-temperature spectra of ethene, propene and but-1-ene on Pt/SiO2 all exhibited prominent absorptions from the n-alkylidyne, but other adsorbed species also contributed to the spectra, considered to be predominantly the appropriate di-σ species PtCH2CH(R)Pt (R = H, CH3, C2H5) together with smaller amounts of the relevant π-complexes. In the case of the cis- and trans-but-2-enes, virtually identical spectra were obtained on Pt/SiO2 but with many of the same prominent features as from but-1-ene. Clearly the finely divided catalyst had sites which led to double-bond isomerization. A smaller proportion of di-σ/π bonded but-2-yne was also present.The infrared spectra proved to be very effective at delineating the similarities and differences between the species chemisorbed on Pt(111) and on the Pt/SiO2 catalyst.

The standard enthalpies of formation of some aliphatic diols

Abstract Energies of combustion of HO(CH2)nOH (n = 2 to 6), DL-propan-1,2-diol, DL-butan-1,3-diol, and 2,2-dimethylpropan-1,3-diol have been determined by static bomb calorimetry. The standard enthalpies of formation of the condensed phases are derived and in combination with enthalpies of transition obtained ebullioscopically, corresponding values for the gas phase are calculated.

The thermal denaturation of collagen fibres swollen in aqueous solutions of urea, hexamethylenetetramine, p-benzoquinone and tetra-alkylammonium salts

Abstract The effect of urea, hexamethylenetetramine, p -benzoquinone, and tetra-alkylammonium salts on the enthalpy and temperature of denaturation of swollen collagen fibres was studied using differential scanning calorimetry. The results obtained suggest that hydrophobic interactions plays a significant role in stabilizing insoluble collagen, and may account for about 25% of the total stabilizing energy.

Thermochemistry of picrates. I. The standard enthalpy of formation of ammonium picrate

Abstract Using a static, oxygen-bomb calorimeter, the standard enthalpy of combustion at 298.15 K of the yellow crystalline modification of ammonium picrate has been determined as −2833.11 ± 2.83 kJ mole −1 . The standard enthalpy of formation is −385.44 ± 2.94 kJ mole −1 . These results are discussed in relation to previous values and also in connexion with solution calorimetric studies involving picric acid and metal picrates.

Enthalpy changes associated with the denaturation of collagens of different imino acid content

The enthalpy changes associated with the denaturation of acid-soluble and insoluble collagens prepared from sheep, cod, halibut and pike skin were determined by differential scanning calorimetry. The enthalpy change associated with the soluble collagens decreased with decreasing imino acid content (from 1420 cal/mol for sheep to 736 cal/mol for cod) while the value for insoluble collagens was approximately constant at 1360 cal/mol. A possible explanation for these values in terms of the nautre of the bonds present in collagen is discussed.

Thermodynamics of the zinc sulphide transformation, sphalerite → wurtzite, by modified entrainment

The dissociative sublimation of both α- and β-zinc sulphide, ZnS(c)= Zn(g)+½S2(g), has been studied by modified entrainment in the temperature range 1010–1445 K. The following free-energy equations were derived: ΔG°(α)/J mol–1= 376 700 – 191.9T/K and ΔG°(β)/J mol–1= 374 200 – 190.4T/K from which the enthalpy and entropy changes of transformation (β→α) at the transition temperature (1293 K) were –2.5 ± 1.5 kJ mol–1 and –1.5 ± 1.3 J K–1 mol–1. The corresponding ΔH°(β→α) at 298.15 K obtained by the third-law method was –2.3 ± 0.9 kJ mol–1. This enthalpy change is at variance with the currently accepted value of ca. 13 kJ mol–1.

Thermodynamic functions for the congruent sublimation of cadmium telluride

Using a modified entrainment method the enthalpy and entropy changes for the reaction CdTe(c) ⇋ Cd(g)+0.5 Te2(g) at 298.15 K were determined as 72.0 ± 0.9 kcal mol-1 and 51.0 ± 0.8 cal K-1 mol-1, respectively, both values being significantly higher than previous estimates.

The phosphorus-phosphorus bond energy in diphosphorus tetra-iodide

Abstract The enthalpies of sublimation at 298·15 K of phosphorus tri-iodide and diphosphorus tetra-iodide (15·2 ± 0·9 and 16·7 ± 0·5 kcal.mole −1 respectively) have been determined using an effusion manometer. Combination of these enthalpies with literature thermodynamic data gives an estimate of 62 kcal for the phosphorus-phosphorus bond energy in P 2 I 4 .

The retarded sublimation of red phosphorus

Vaporization coefficients for red phosphorus (form IV) were determined to the range 620–690 K at phosphorus saturation ratios (p*/p°) of 0.08–0.29 and in the presence of nitrogen at ca. 1 atm. At 650 K, αv(p*/p°= 0.18)= 2.5 × 10–8. The effect of iodine on the sublimation rate was examined.

The standard enthalpies of combustion and formation of crystalline phenylphosphonic, phenylphosphinic, and diphenylphosphinic acids

The standard enthalpies of formation of crystalline phenylphosphinic (C6H5PO2H2), phenylphosphonic (C6H5PO3H2), and diphenylphosphinic ((C6H5)2PO2H) acids were determined as −(133.3 ± 4.9), −(212.6 ± 2.6), and −(124.2 ± 5.8) kcalth mol−1 at 298.15 K respectively by a combustion-calorimetric method. The difference between the first two enthalpies of formation, (79.3 ± 5.5) kcalth mol−1, was confirmed independently as (79.0 ± 0.5) kcalth mol−1 by a solution-calorimetric technique.